The nuchal translucency (NT) scan is usually the first detailed look at your baby. It is done between 11 weeks and 13 weeks 6 days, when the baby measures 45 to 84 mm from head to bottom (the crown–rump length, or CRL). Outside this window the NT measurement cannot be used for screening, so it is worth booking as soon as your dating scan has given you a due date.
Every baby has a thin layer of fluid under the skin at the back of the neck. Measured to a tenth of a millimetre and combined with your age, the baby’s heart rate and a blood test, it gives an individual chance for Down syndrome and two other trisomies. The same scan checks early anatomy, confirms the number of babies, settles whether twins share a placenta and, with a few extra measurements, estimates your risk of pre-eclampsia.
Dr. Devang Patel holds NT scan accreditation from the Fetal Medicine Foundation (UK), which means measurements are taken to an audited international protocol. Scans are performed at Divine Women’s Hospital, Gota, and the result is explained by the consultant in the same visit, in Gujarati, Hindi or English.
What the nuchal translucency is, and why it matters
The nuchal translucency is a normal collection of fluid seen as a dark band behind the baby’s neck in the first trimester. It is present in every baby and usually disappears by around 14 weeks, which is why the scan has a strict window.
Babies with chromosomal conditions such as Down syndrome tend to have a thicker NT, and so do some babies with heart conditions, certain genetic syndromes and problems with the lymphatic system. The NT is therefore a marker of chance, not a diagnosis. Most babies with a slightly thicker NT are perfectly healthy.
What is checked during the scan
- Crown–rump length, which confirms or corrects your due date
- Nuchal translucency, measured to the FMF protocol with the baby in a neutral position and the image magnified
- Heartbeat and heart rate, and the number of babies
- In twins, chorionicity: whether they share one placenta (monochorionic) or have two (dichorionic), which is most accurate before 14 weeks
- Early anatomy: skull and brain, face, spine, abdominal wall, stomach, bladder, arms and legs, and heart views where possible
- Additional markers where helpful: the nasal bone, blood flow across the tricuspid valve and in the ductus venosus
- Uterine artery Doppler and your blood pressure, used for pre-eclampsia screening
Around 40–50% of major structural conditions can already be suspected at a careful 11–14 week scan, though the anomaly scan at 18–22 weeks is still essential.
How combined screening produces your result
In combined first-trimester screening, the NT is put together with your age, the CRL, the baby’s heart rate and two hormones in your blood, free beta-hCG and PAPP-A. The Fetal Medicine Foundation algorithm then gives a separate chance for trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome), written as a figure such as 1 in 8,000 or 1 in 60.
Most centres use a cut-off of around 1 in 100 to 1 in 150 for a higher-chance result. Results between about 1 in 100 and 1 in 1,000 are sometimes called intermediate, and for these, NIPT is a sensible next step. Your weight, ethnicity, smoking, diabetes and IVF conception all adjust the blood hormone values, so accurate details on the form matter.
| Screening option | What it uses | Detection of Down syndrome |
|---|---|---|
| Age alone | Mother’s age | About 30% (at a 5% screen-positive rate) |
| NT + age | Scan measurement and age | About 75–80% |
| Combined test | NT, age, free beta-hCG, PAPP-A | About 90%, with 5% screen-positive |
| Combined + extra markers | Adds nasal bone, tricuspid and ductus venosus flow | About 93–95%, with fewer false positives |
| NIPT (cell-free DNA) | Placental DNA in mother’s blood | About 99%, with around 0.1% false positives |
Pre-eclampsia screening at the same visit
Pre-eclampsia is a common and serious complication in India, and its early form, needing delivery before 34 weeks, is the most dangerous. At the NT visit your history, blood pressure in both arms, uterine artery Doppler and the PAPP-A level (or PlGF where available) are combined to estimate your individual risk.
If the risk is 1 in 100 or higher, low-dose aspirin (usually 150 mg at night) started before 16 weeks and continued to 36 weeks reduced preterm pre-eclampsia by about 60% in the large ASPRE trial. This is one of the most useful things the first-trimester scan can offer, whatever the chromosomal result.
If your result is higher chance or the NT is increased
A higher-chance result is a reason for a calm conversation, not for alarm. Even with a result of 1 in 50, 49 out of 50 such pregnancies do not have the condition. At a counselling visit you will discuss what the figure means and your choices: NIPT, chorionic villus sampling (CVS) from 11 weeks, amniocentesis from 15 weeks, or no further testing.
When the NT is 3.5 mm or more (above the 99th centile), diagnostic testing with chromosomal microarray is usually discussed directly rather than NIPT, because a thick NT can be linked to smaller chromosomal changes and genetic syndromes that NIPT does not cover. An early fetal echo around 16 weeks and a detailed anomaly scan follow. When the chromosomes and these scans are normal, the large majority of babies are born well.
Limits of the NT scan
The NT scan is a screening test with false positives and false negatives. About 1 in 10 babies with Down syndrome will be in the low-chance group, and some structural conditions develop later or are too small to see at 12 weeks.
The measurement can occasionally not be obtained because of the baby’s position, your body build or a retroverted uterus. A short walk, a second attempt, or a vaginal scan usually solves this. If it still cannot be measured, other screening options are discussed.
Twins and IVF pregnancies
In twins, each baby has its own NT, and the chance is calculated for each one. Determining chorionicity at this scan is crucial, because monochorionic twins need scans every two weeks from 16 weeks to look for twin-to-twin transfusion syndrome.
After IVF or ICSI, the due date is taken from the embryo transfer date rather than the CRL. Hormone levels can differ slightly in IVF pregnancies, and the algorithm corrects for this, which is why the method of conception is recorded on the form.
How the NT visit is organised at Divine Women’s Hospital
The NT scan is booked as a consultant appointment rather than a quick slot, because the measurement, the calculation and the conversation all take time. The FMF-accredited measurement is taken by Dr. Devang Patel himself, and the combined risk is calculated once the blood values are available, usually on the same day.
Bring your dating scan report, any earlier pregnancy records, a list of medicines and, if you have diabetes or thyroid disease, your latest results. Your husband or a family member is welcome to join the explanation, and the discussion can happen in Gujarati, Hindi or English, whichever you are most comfortable with.
If the result is low chance, your next visit is planned around the anomaly scan at 18–22 weeks. If it is higher chance, or the pre-eclampsia risk is raised, a counselling visit or an aspirin plan is arranged before you leave, so nothing is left waiting over a weekend.
A note on the PCPNDT Act
Pre-natal sex determination is prohibited in India under the PCPNDT Act. The sex of the baby is not detected or disclosed at any scan.
Your care, step by step
- Book at the right weekYour appointment is timed from the dating scan so that the baby falls within the 45–84 mm window, ideally at 12–13 weeks.
- Blood sampleFree beta-hCG and PAPP-A are taken on the day or a few days before; your weight, history and medicines are recorded for the calculation.
- The scanNT, early anatomy and Dopplers are checked, usually through the abdomen. A brief vaginal scan is sometimes used for a clearer view.
- Result and explanationYour individual chances for trisomies and pre-eclampsia are explained in the same visit, with a written report.
- Plan for what comes nextAspirin, NIPT, counselling, an early heart scan or the anomaly scan at 18–22 weeks is booked before you leave.
When to book a visit
- You are between 11 weeks and 13 weeks 6 days of pregnancy, or will be soon
- You are 35 or older, or conceived through IVF or ICSI
- A previous baby had a chromosomal, genetic or structural condition
- You are expecting twins and need chorionicity confirmed
- You had pre-eclampsia before, or have high blood pressure, diabetes, kidney disease or APLA
- You are unsure of your dates and want an accurate due date
Warning signs - get same-day care
- Heavy vaginal bleeding, soaking a pad in an hour, or passing clots
- Severe or one-sided lower abdominal pain, especially with dizziness or shoulder-tip pain
- Fainting, a racing heartbeat or feeling very unwell
- Fever above 38 °C with abdominal pain or foul-smelling discharge
- Persistent vomiting with inability to keep fluids down for more than 24 hours
Labour and emergency care are available 24 × 7. Call the hospital and come in directly.
Myths and facts
Myth: A normal NT scan means the baby cannot have Down syndrome.
It means the chance is low, not zero. Screening detects about 90% of cases, and only a diagnostic test gives a definite answer.
Myth: If NIPT is done, the NT scan is unnecessary.
NIPT does not check anatomy, chorionicity in twins or pre-eclampsia risk. The NT scan remains useful whichever blood test you choose.
Myth: A thick NT means the baby has a problem.
A thicker NT raises the chance of some conditions, but most babies with an increased NT and normal follow-up tests are healthy.
Myth: Ultrasound in early pregnancy harms the baby.
Diagnostic ultrasound used within standard safety settings has no proven harmful effect, and the scan is kept as short as needed.
Frequently asked questions
What is the normal NT measurement at 12 weeks?
The normal range rises a little as the baby grows. At 12 weeks most babies measure around 1 to 2 mm, the 95th centile is roughly 2.2 to 2.5 mm across the window, and 3.5 mm or more is above the 99th centile. The value is always combined with your age and blood test.
What is the right week for the NT scan?
Any time from 11 weeks 0 days to 13 weeks 6 days. Around 12 to 13 weeks is usually ideal, as the anatomy is easier to see while still well inside the window.
Is the double marker test the same as the NT scan?
The double marker is the blood part of combined screening (free beta-hCG and PAPP-A). It is far more useful when combined with the NT measurement, so the two are done together.
Do I need a full bladder for the NT scan?
A comfortably full bladder can help early in pregnancy, but an overfull bladder is uncomfortable and not needed. The team will advise you when you book.
Should I fast before the NT scan blood test?
No. Free beta-hCG and PAPP-A are not affected by food, so you can eat and drink normally.
What does a 1 in 250 result mean?
It means that out of 250 women with the same result, one would have a baby with the condition and 249 would not. Whether to test further depends on the cut-off used and on your own views, which are discussed with you.
Can the NT scan detect heart defects?
It can raise suspicion through a thick NT, abnormal tricuspid or ductus venosus flow, or an early heart view. A full assessment needs a fetal echo, usually at 18–24 weeks or earlier when needed.
I missed the NT window. What now?
After 14 weeks, NIPT or second-trimester blood screening (the quadruple test) can be used, followed by the anomaly scan at 18–22 weeks. Pre-eclampsia screening is less useful after 16 weeks.
Is the NT scan safe for my baby?
Yes. It is a standard ultrasound scan with no radiation and no needle for the baby.